Along with the progress of medical technology in recent years, the number of cases where cardiopathy which has been considered as a serious disease can be cured is increased. On the other hand, with respect to serious cardiopathy, at present, there may be also a case where the only way to cure such cardiopathy is the heart transplantation. Under such circumstances, a heart transplantation waiting patient has to wait for a donor who is compatible with the patient. Accordingly, there has been also a case where the heart transplantation cannot be promptly carried out so that the life support of the heart transplantation waiting patient is heavily hindered.
To cope with such a situation, there has been adopted a method in which an auxiliary artificial heart is embedded in such a heart transplantation waiting patient so as to assist the circulation of blood of the patient thus allowing the heart transplantation waiting patient to wait for a donor who is compatible with the patient for a long period. It is expected that the life of a patient which suffers from serious cardiopathy is helped not by a heart of a donor but by an artificial heart in future.
Such an auxiliary artificial heart includes an auxiliary artificial heart pump which functions as a blood pump for assisting functions of a left ventricle and a right ventricle. The auxiliary artificial heart is a so-called life support device and hence, the auxiliary artificial heart pump and an auxiliary artificial heart pump drive device for driving the auxiliary artificial heart pump are requested to exhibit extremely high reliability and availability.
Techniques which are applicable to enhance the reliability and availability of the auxiliary artificial heart pump drive device are disclosed in patent document 1, patent document 2, patent document 3 and non-patent document 1, for example. Patent document 1 discloses an inverter device for driving an AC motor in which control parts are duplexed and the control parts are changed over so as to prevent the flow of an overcurrent. Patent document 2 discloses an electric vehicle control device in which microprocessors which perform a vehicle control are provided doubly, and arithmetic calculation results of the respective microprocessors are checked doubly thus outputting a normal arithmetic calculation result. Patent document 3 discloses a technique relating to a motor drive circuit which includes a main drive circuit and a backup drive circuit for driving a motor, and outputs a drive signal of either one of the main drive circuit and the backup drive circuit to a motor using a switching circuit when a failure is detected in the main drive circuit. Non-patent document 1 discloses a redundant motor which includes motor windings of two systems in the motor.    Patent document 1: JP-A-7-231697    Patent document 2: JP-A-7-143604    Patent document 3: JP-A-2007-83887    Non-patent document: N. Ertugrul, W. Soong, G. Dostal and D. Saxon, “Fault Tolerant Motor Drive System with Redundancy for Critical Application”, IEEE Power Electronics Specialists Conference, 2002, p. 1457-1462